outlet vs spiracle

outlet

noun
  • A vent or similar passage to allow the escape of something. 

  • A river that runs out of a lake. 

  • Something which allows for the release of one's desires. 

  • A shop that sells the products of a particular manufacturer or supplier. 

  • A wall-mounted device such as a socket or receptacle connected to an electrical system at which current is taken to supply utilization equipment or appliances. 

spiracle

noun
  • Any small aperture or vent for air or other fluid. 

  • A pore or opening used (especially by arthropods and some fish) for respiration. 

  • The blowhole of a whale, dolphin or other similar species. 

How often have the words outlet and spiracle occurred in a corpus of books? (source: Google Ngram Viewer )